Novel hydrophilic-hydrophobic block copolymer based on cardo poly(arylene ether sulfone)s with bis-quaternary ammonium moieties for anion exchange membranes

• Block and random copolymers bearing bis-quaternary ammonium were synthesized.
• Block copolymer exhibited higher ionic conductivity and alkaline stability.
• Block copolymer exhibited higher fuel cell performance.

Two types of phenolphthalein-based copolymers, random and block cardo poly(aryl ether sulfone)s with pendant tertiary amine groups were synthesized via copolycondensation. Both of the copolymers were grafted with (3-bromopropyl) trimethylammonium bromide to prepare anion exchange membranes with bis-quaternary ammonium groups for hydroxide ion conductivity measurements. The block anion exchange membrane QBPES-60 with an ion exchange capacity (IEC) of 1.93 mmol g−1 exhibited higher ionic conductivity (40.5 mS cm−1) in water at 60 °C than the random copolymer QRPES-60 (30.0 mS cm−1) under the same conditions. Small-angle X-ray scattering and transmission electron microscopy suggested the membrane constructed from the block polymer exhibited a more obvious phase-separated structure and formed ion clusters which would be responsible for the high conductivity. Moreover, the block anion exchange membrane with bis-quaternary ammonium groups showed better alkaline stability than the random membrane where degradation could be recognized by 1H NMR spectra as well as ion conductivities. In conclusion, integrating the block hydrophilic bis-quaternary ammonium ion groups along with the long aliphatic side chains, and the hydrophobic copolymer backbone, this synthetic strategy is promising to prepare AEMs with high conductivity and good alkaline stability.

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